Combination scanner and tracker device having a focusing mechanism

ABSTRACT

A three-dimensional (3D) coordinate measurement device combines tracker and scanner functionality. The tracker function is configured to send light to a retroreflector and determine distance to the retroreflector based on the reflected light. The tracker is also configured to track the retroreflector as it moves, and to determine 3D coordinates of the retroreflector. The scanner is configured to send a beam of light to a point on an object surface and to determine 3D coordinate of the point. In addition, the scanner is configured to adjustably focus the beam of light.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part application of U.S.patent application Ser. No. 13/765,014 entitled “Multi-Mode OpticalMeasurement Device and Method of Operation” filed 12 Feb. 2013, thecontents of which are incorporated by reference herein in theirentirety.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates to an optical measurementdevice that measures dimensional coordinates, and in particular to anoncontact optical measurement device have multiple optical devices formeasuring an object.

Noncontact optical measurement devices may be used to determine thecoordinates of points on an object. One type of optical measurementdevice measures the three-dimensional (3D) coordinates of a point bysending a laser beam to the point. The laser beam may impinge directlyon the point or on a retroreflector target in contact with the point. Ineither case, the instrument determines the coordinates of the point bymeasuring the distance and the two angles to the target. The distance ismeasured with a distance-measuring device such as an absolute distancemeter or an interferometer. The angles are measured with anangle-measuring device such as an angular encoder. A gimbaledbeam-steering mechanism within the instrument directs the laser beam tothe point of interest.

The laser tracker is a particular type of coordinate-measuring devicethat tracks the retroreflector target with one or more laser beams itemits. Optical measurement devices closely related to the laser trackerare the laser scanner and the total station. The laser scanner steps oneor more laser beams to points on a surface. It picks up light scatteredfrom the surface and from this light determines the distance and twoangles to each point. The total station, which is most often used insurveying applications, may be used to measure the coordinates ofdiffusely scattering (noncooperative) targets or retroreflective(cooperative) targets.

The laser tracker operates by sending a laser beam to a retroreflectortarget that is used to measure the coordinates of specific points. Acommon type of retroreflector target is the spherically mountedretroreflector (SMR), which comprises a cube-corner retroreflectorembedded within a metal sphere. The cube-corner retroreflector comprisesthree mutually perpendicular mirrors. The vertex, which is the commonpoint of intersection of the three mirrors, is located at the center ofthe sphere. Since the placement of the cube corner within the sphere hasa known mechanical relationship to the measured point (i.e. theperpendicular distance from the vertex to any surface on which the SMRrests remains constant, even as the SMR is rotated) the location of themeasured point may be determined Consequently, the laser tracker canmeasure the 3D coordinates of a surface by following the position of anSMR as it is moved over the surface. Stating this another way, the lasertracker needs to measure only three degrees of freedom (one radialdistance and two angles) to fully characterize the 3D coordinates of asurface.

One type of laser tracker contains only an interferometer (IFM) withoutan absolute distance meter (ADM). If an object blocks the path of thelaser beam from one of these trackers, the IFM loses its distancereference. The operator must then track the retroreflector to a knownlocation to reset to a reference distance before continuing themeasurement. A way around this limitation is to include an ADM in thetracker. The ADM can measure distance in a point-and-shoot manner.

Since trackers dwell on a point, it is desirable to place a constrainton laser power to maintain a desired categorization within the IEC60825-1 standard. Thus it is desired that the tracker work at low laserpower. In addition to clearly defining the measurement point, the SMRreturns a large fraction of the laser power. In contrast, a laserscanner may be arranged to move continuously, this allows a desirableIEC 60825-1 categorization since total energy deposited on a portion ofa person located in the area of operation is small. Thus, laser scannerscan operate at higher laser power levels and operate withnon-cooperating targets, albeit typically at lower accuracy and shorterdistances than a laser tracker.

The laser scanner also sends out a laser beam toward an object. Sincelaser trackers interact with the operator (via the retroreflectortarget), it is desirable for the laser to be visible. However, laserscanners may be operated at other wavelengths—for example, infrared orvisible wavelengths since the operator does not need to visually see thelight beam. The laser scanner receives light reflected back from theobject and determines the distance to the point on the object based inpart on the time of flight for the light to strike the object and returnto the scanner. Some laser scanners sequentially rotate about a zenithaxis and simultaneously rotating the laser beam about the azimuth axis,the coordinates for points in the area about the laser scanner may bedetermined Other laser scanners direct a beam of light to a single pointor in a predetermined pattern, such as a raster patter for example.

It should be appreciated that the laser scanner may obtain thecoordinates for a plurality of points much faster than a laser tracker.However, the laser tracker will measure the distance with a higheraccuracy. Further, since laser trackers dwell on specific points,measurements typically integrate for fractions of a second to reduce thenoise in the electronics and atmospheric turbulence. Since laserscanners typically measure on the order of a million points per second,measurements are typically made in the order of microseconds orfractions of a microsecond. Thus in scanners the noise resulting fromelectronics and atmospheric turbulence may be much greater.

Accordingly, while existing noncontact optical measurement devices aresuitable for their intended purposes the need for improvement remains,particularly providing an optical measurement device that allows anoperator to select between multiple modes of operation.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the invention, a coordinate measurementdevice includes: an optical delivery system; a first absolute distancemeter including a first light source, a first optical detector, and afirst electrical circuit, the first light source configured to send afirst light through the optical delivery system to a retroreflectortarget, the first optical detector further configured to generate afirst electrical signal in response to the first light reflected by theretroreflector target and to transmit the first electrical signal to thefirst electrical circuit, the first electrical circuit configured todetermine a first distance from the coordinate measurement device to theretroreflector target based at least in part on the first electricalsignal; a second absolute distance meter including a second lightsource, an adjustable focusing mechanism, a second optical detector, anda second electrical circuit, the second light source configured to senda second light through the adjustable focusing mechanism and the opticaldelivery system to an object surface, the second optical detectorconfigured to receive the second light reflected by the object surfaceand passed through the optical delivery system, the second opticaldetector further configured to generate a second electrical signal inresponse to the second light reflected by the object surface and to sendthe second electrical signal to the second electrical circuit, thesecond electrical circuit configured to determine a second distance fromthe coordinate measurement device to the object surface based at leastin part on the second electrical signal; a structure operably coupled tothe optical delivery system, the first absolute distance meter, and thesecond absolute distance meter; a first motor configured to rotate thestructure about a first axis; a first angular transducer operablycoupled to the structure, the first angular transducer configured tomeasure a first angle of rotation about the first axis; a second motorconfigure to rotate the structure about a second axis, the second axisbeing substantially perpendicular to the first axis; a second angulartransducer operably coupled to the structure, the second angulartransducer configured to measure a second angle of rotation about thesecond axis; a position detector, the position detector configured toreceive a portion of radiation emitted by the coordinate measurementdevice and reflected by the retroreflector target, the position detectorconfigured to generate a third electrical signal based at least in parton a location at which the portion of radiation strikes the positiondetector; and a processor, the processor having computer readable mediaconfigured to operate in a first mode and a second mode, wherein thefirst mode includes tracking the retroreflector target based at least inpart on the third electrical signal, and determining a firstthree-dimensional coordinate of the retroreflector target based at leastin part on the first angle of rotation to the retroreflector target at afirst position, the second angle of rotation to the retroreflectortarget at the first position, and the first distance of theretroreflector target at the first position, and wherein the second modeincludes directing the second light to the object surface anddetermining a second three-dimensional coordinate of a point on theobject surface based at least in part on the first angle of rotation tothe point on the object surface, the second angle of rotation to thepoint on the object surface, and the second distance of the point on theobject surface, the second mode further including adjusting theadjustable focusing mechanism.

According to another aspect of the invention, a coordinate measurementdevice comprises: a structure; a first motor configured to rotate thestructure about a first axis; a first angular transducer operablycoupled to the structure, the first angular transducer configured tomeasure a first angle of rotation about the first axis; a second motorconfigure to rotate the structure about a second axis, the second axisbeing substantially perpendicular to the first axis, a projection of thesecond axis intersecting a projection of the first axis in a gimbalpoint; a second angular transducer operably coupled to the structure,the second angular transducer configured to measure a second angle ofrotation about the second axis; an optical delivery system operablycoupled to the structure; a first absolute distance meter operablycoupled to the structure, the first absolute distance meter including afirst light source, a first optical detector, and a first electricalcircuit, the first light source configured to send a first light throughthe optical delivery system along a portion of a first line that extendsfrom the gimbal point to a retroreflector target, the first line beingperpendicular to the first axis, the first optical detector configuredto receive the first light reflected by the retroreflector target andpassed through the optical delivery system, the first optical detectorfurther configured to generate a first electrical signal in response tothe first light reflected by the retroreflector target and to transmitthe first electrical signal to the first electrical circuit, the firstelectrical circuit configured to determine a first distance from thecoordinate measurement device to the retroreflector target based atleast in part on the first electrical signal; a second absolute distancemeter operably coupled to the structure, the second absolute distancemeter including a second light source, an adjustable focusing mechanism,a second optical detector, and a second electrical circuit, the secondlight source configured to send a second light through the adjustablefocusing mechanism and the optical delivery system along a portion of asecond line that extends from the gimbal point to an object surface, thesecond line being perpendicular to the first axis, the second line beingdifferent than the first line, the second optical detector configured toreceive the second light reflected by the object surface and passedthrough the optical delivery system, the second optical detector furtherconfigured to generate a second electrical signal in response to thesecond light reflected by the object surface and to send the secondelectrical signal to the second electrical circuit, the secondelectrical circuit configured to determine a second distance from thecoordinate measurement device to the object surface based at least inpart on the second electrical signal; a position detector, the positiondetector configured to receive a portion of radiation emitted by thecoordinate measurement device and reflected by the retroreflectortarget, the position detector configured to generate a third electricalsignal based at least in part on a location at which the portion ofradiation strikes the position detector; and a processor, the processorhaving computer readable media configured to operate in a first mode anda second mode, wherein the first mode includes tracking theretroreflector target based at least in part on the third electricalsignal, and determining a first three-dimensional coordinate of theretroreflector target based at least in part on the first angle ofrotation to the retroreflector target at a first position, the secondangle of rotation to the retroreflector target at the first position,and the first distance of the retroreflector target at the firstposition, and wherein the second mode includes rotating the structureabout the first axis and determining a second three-dimensionalcoordinate of a point on the object surface based at least in part onthe first angle of rotation to the point on the object surface, thesecond angle of rotation to the point on the object surface, and thesecond distance of the point on the object surface, the second modefurther including adjusting the adjustable focusing mechanism.

According to another aspect of the invention, a coordinate measurementdevice includes: an optical delivery system; a first absolute distancemeter including a first light source, a first optical detector, and afirst electrical circuit, the first light source configured to send afirst light through the optical delivery system to a retroreflectortarget, the first optical detector configured to receive the first lightreflected by the retroreflector target and passed through the opticaldelivery system, the first optical detector further configured togenerate a first electrical signal in response to the first lightreflected by the retroreflector target and to transmit the firstelectrical signal to the first electrical circuit, the first electricalcircuit configured to determine a first distance from the coordinatemeasurement device to the retroreflector target based at least in parton the first electrical signal; a second absolute distance meterincluding a second light source, an adjustable focusing mechanism, asecond optical detector, and a second electrical circuit, the secondlight source configured to send a second light through the adjustablefocusing mechanism and the optical delivery system to an object surface,the second optical detector configured to receive the second lightreflected by the object surface and passed through the optical deliverysystem, the second optical detector further configured to generate asecond electrical signal in response to the second light reflected bythe object surface and to send the second electrical signal to thesecond electrical circuit, the second electrical circuit configured todetermine a second distance from the coordinate measurement device tothe object surface based at least in part on the second electricalsignal; a structure operably coupled to the optical delivery system, thefirst absolute distance meter, and the second absolute distance meter,the structure including a mirror mounted for rotation, the mirror beingarranged within an optical path of the first light and the second light;a first motor configured to rotate the structure about a first axis; afirst angular transducer operably coupled to the structure, the firstangular transducer configured to measure a first angle of rotation aboutthe first axis; a second motor configured to rotate the mirror about asecond axis, the second axis being substantially perpendicular to thefirst axis; a second angular transducer operably coupled to the mirror,the second angular transducer configured to measure a second angle ofrotation about the second axis; a position detector, the positiondetector configured to receive a portion of radiation emitted by thecoordinate measurement device and reflected by the retroreflectortarget, the position detector configured to generate a third electricalsignal based at least in part on a location at which the portion ofradiation strikes the position detector; and a processor, the processorhaving computer readable media configured to operate in a first mode anda second mode, wherein the first mode includes tracking theretroreflector target based at least in part on the third electricalsignal, and determining a first three-dimensional coordinate of theretroreflector target based at least in part on the first angle ofrotation to the retroreflector target at a first position, the secondangle of rotation to the retroreflector target at the first position,and the first distance of the retroreflector target at the firstposition, and wherein the second mode including rotating the structureabout the first axis and determining a second three-dimensionalcoordinate of a point on the object surface based at least in part onthe first angle of rotation to the point on the object surface, thesecond angle of rotation to the point on the object surface, and thesecond distance of the point on the object surface, the second modefurther including adjusting the adjustable focusing mechanism.

These and other advantages and features will become more apparent fromthe following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWING

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1 is a perspective illustration of an optical measurement device inaccordance with an embodiment of the invention;

FIG. 2 is a partial perspective illustration of the optical measurementdevice of FIG. 1 illustrating the location of a tracker and scannerportions, including sensors within the device;

FIG. 3 is a block diagram of the electrical and computing system for thedevice of FIG. 1;

FIG. 4 is a schematic illustration of the device of the payload portionof FIG. 1 including a block diagram of the of the optical measurementdevice in accordance with an embodiment of the invention;

FIGS. 5-10 are block diagrams of electrical and electro-optical elementswithin an absolute distance meter (ADM) for a laser tracker portion anda scanner distance meter of the optical measurement device of FIG. 1;

FIG. 11 is a schematic illustration of the device of FIG. 1 showing anoptical axis along which light from the tracker and scanner isprojected;

FIGS. 12-14 are perspective views of the device of the FIG. 1illustrating another embodiment of the scanner portion and the trackerportion;

FIG. 15 is a schematic illustration of an optical measurement device ina first mode of operation in accordance with an embodiment of theinvention;

FIG. 16 is a schematic illustration of the optical measurement device ofFIG. 1 in a second mode of operation; and

FIGS. 17-18 are flow diagrams showing the steps for operating theoptical measurement device;

FIG. 19 shows an apparatus that emits tracker light and scanner light intwo different directions from the scanner-tracker according to anembodiment;

FIG. 20 is a schematic illustration of a scanner-tracker device thatuses a rotating mirror to direct a beam of light from the tracker to aretroreflector according to an embodiment of the invention;

FIG. 21. is a schematic illustration of the device payload portion ofFIG. 1 including a block diagram of the of the optical measurementdevice in accordance with an embodiment of the invention;

FIG. 22 is a schematic illustration of the device of FIG. 1 showing anoptical axis along which light from the tracker and scanner isprojected;

FIG. 23 is a schematic illustration of an optical measurement device ina first mode of operation in accordance with an embodiment of theinvention;

FIG. 24 is a schematic illustration of the optical measurement device ofFIG. 1 in a second mode of operation;

FIG. 25 shows an apparatus that emits tracker light and scanner light intwo different directions from the scanner-tracker according to anembodiment; and

FIG. 26 is a schematic representation of an adjustable focusingmechanism according to an embodiment.

The detailed description explains embodiments of the invention, togetherwith advantages and features, by way of example with reference to thedrawings.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention provide for an optical measurementdevice that may operate as either a laser tracker or a laser scanner.This provides advantages in allowing either a higher accuracymeasurement using a cooperative target, usually handheld by an operator,or a faster (usually) lower accuracy measurement, usually without theactive assistance of an operator. These two modes of operation areprovided in a single integrated device.

Referring now to FIGS. 1-2, an optical measurement device 30 is shownthat provides for multiple modes of operation. The device 30 has ahousing 32 containing tracker portion 34 to support laser trackingfunctionality and a scanner portion 36 to support scanner functionality.An exemplary gimbaled beam steering mechanism 38 includes a zenithcarriage 42 mounted on an azimuth base 40 and rotated about an azimuthaxis 44. A payload structure 46 is mounted on the zenith carriage 42,which rotates about a zenith axis 48. The zenith axis 48 and the azimuthaxis 44 intersect orthogonally, internally to device 30, at the gimbalpoint 50. The gimbal point 50 is typically the origin for distance andangle measurements. One or more beams of light 52 virtually pass throughthe gimbal point 50. The emerging beams of light are pointed in adirection orthogonal to zenith axis 48. In other words, the beam oflight 52 lies in a plane that is approximately perpendicular to thezenith axis 48 and that contains the azimuth axis 44. The outgoing lightbeam 52 is pointed in the desired direction by rotation of payloadstructure 46 about a zenith axis 48 by rotation of zenith carriage 40about the azimuth axis 44.

A zenith motor 51 and zenith angular encoder 54 are arranged internal tothe housing 32 and is attached to the zenith mechanical axis aligned tothe zenith axis 48. An azimuth motor 55 and angular encoder 56 are alsoarranged internal to the device 30 and is attached to an azimuthmechanical axis aligned to the azimuth axis 44. The zenith and azimuthmotors 51, 55 operate to rotate the payload structure 46 about the axis44, 48 simultaneously. As will be discussed in more detail below, inscanner mode the motors 51, 55 are each operated in a single directionwhich results in the scanner light following a continuous pathway thatdoes not reverse direction. The zenith and azimuth angular encodersmeasure the zenith and azimuth angles of rotation to relatively highaccuracy.

The light beam 52 travels to target 58 which reflects the light beam 53back toward the device 30. The target 58 may be a noncooperative target,such as the surface of an object 59 for example. Alternatively, thetarget 58 may be a retroreflector, such as a spherically mountedretroreflector (SMR) for example. By measuring the radial distancebetween gimbal point 50 and target 58, the rotation angle about thezenith axis 48, and the rotation angle about the azimuth axis 44, theposition of the target 58 may be found within a spherical coordinatesystem of the device 30. As will be discussed in more detail herein, thedevice 30 includes one or more mirrors, lenses or apertures that definean optical delivery system that directs and receives light.

The light beam 52 may include one or more wavelengths of light, such asvisible and infrared wavelengths for example. It should be appreciatedthat, although embodiments herein are discussed in reference to thegimbal steering mechanism 38, other types of steering mechanisms may beused. In other embodiments a mirror may be rotated about the azimuth andzenith axes for example. In other embodiments, galvo mirrors may be usedto steer the direction of the light. Similar to the exemplaryembodiment, these other embodiments (e.g. galvo mirrors) may be used tosteer the light in a single direction along a pathway without reversingdirection as is discussed in more detail below.

In one embodiment, magnetic nests 60 may be arranged on the azimuth base40. The magnetic nests 60 are used with the tracker portion 34 forresetting the tracker to a “home position” for different sized SMRs,such as 1.5, ⅞ and 0.5 inch SMRs. And on-device retroreflector 62 may beused to reset the tracker to a reference distance. Further, a mirror(not shown) may be used in combination with the retroreflector 62 toenable performance of self-compensation, as described in U.S. Pat. No.7,327,446, the contents of which are incorporated by reference.

Referring now to FIG. 3, an exemplary controller 64 is illustrated forcontrolling the operation of the device 30. The controller 64 includes adistributed processing system 66, processing systems for peripheralelements 68, 72, computer 74 and other network components 76,represented here is a cloud. Exemplary embodiments of distributedprocessing system 66 includes a master processor 78, payload functionelectronics 80, azimuth encoder electronics 82, zenith encoderelectronics 86, display and user interface (UI) 88, removable storagehardware 90, radio frequency identification (RFID) electronics 92, andantenna 94. The payload function electronics 80 includes a number offunctions such as the scanner electronics 96, the camera electronics 98(for camera 168, FIG. 11), the ADM electronics 100, the positiondetector (PSD) electronics 102, and the level electronics 104. Some orall of the sub functions in payload functions electronics 80 have atleast one processing unit, which may be a digital signal processor (DSP)or a field programmable gate array (FPGA), for example.

Many types of peripheral devices are possible, such as a temperaturesensor 68 and a personal digital assistant 72. The personal digitalassistant 72 may be a cellular telecommunications device, such as asmart phone for example. The device 30 may communicate with peripheraldevices in a variety of means, including wireless communication overantenna 94, by means of vision system such as a camera, and by means ofdistance and angular readings of the laser tracker to a cooperativetarget. Peripheral devices may contain processors. Generally, when theterm scanner processor, laser tracker processor or measurement deviceprocessor is used, it is meant to include possible external computer andcloud support.

In an embodiment, a separate communications medium or bus goes from theprocessor 78 to each of the payload function electronics units 80, 82,86, 88, 90, 92. Each communications medium may have, for example, threeserial lines that include the data line, clock line, and frame line. Theframe line indicates whether or not the electronics unit should payattention to the clock line. If it indicates that attention should begiven, the electronics unit reads the current value of the data line ateach clock signal. The clock signal may correspond, for example, to arising edge of a clock pulse. In one embodiment, information istransmitted over the data line in the form of a packet. In otherembodiments, each package includes an address, a numeric value, a datamessage, and a checksum. The address indicates where, within theelectronics unit, the data messages are to be directed. The locationmay, for example, correspond to a processor subroutine within theelectronics unit. The numeric value indicates the length of the datamessage. The data message contains data or instructions for theelectronics units to carry out. The checksum is a numeric value that isused to minimize the chance of errors in data transmitted over thecommunications line.

In an embodiment, the processor 78 transmits packets of information overthe bus 106 to payload functions electronics 80, over bus 108 to azimuthencoder electronics 82, over bus 110 to zenith encoder electronics 86,over bus 112 to display and UI electronics 88, over bus 114 to removablestorage hardware 90, and over bus 116 to RFID and wireless electronics92.

In an embodiment, the processor 78 also sends a synchronization pulseover the synch bus 118 to each of the electronic units at the same time.The synch pulse provides a way of synchronizing values collected by themeasurement functions of the device 30. For example, the azimuth encoderelectronics 82 in the zenith electronics 86 latch their encoder valuesas soon as the synch pulse is received. Similarly, the payload functionelectronics 80 latch the data collected by the electronics containedwithin the payload structure. The ADM and position detector all latchdata when the synch pulse is given. In most embodiments, the camera andinclinometer collect data at a slower rate than the synch pulse rate butmay latch data at multiples of the synch period.

In one embodiment, the azimuth encoder electronics 82 and the zenithencoder electronics 86 are separated from one another and from thepayload function electronics 80 by slip rings (not shown). Where sliprings are used, the bus lines 106, 108, 110 may be separate buses. Theoptical electronics processing system 66 may communicate with anexternal computer 74, or may provide communication, display, and UIfunctions within the device 30. The device 30 communicates with computer74 over communications link 120, such as an Ethernet line or a wirelessconnection, for example. The device 30 may also communicate with otherelements, represented by cloud 76, over communications link 122, whichmight include one or more electrical cables, such as Ethernet cables forexample, or one or more wireless connections. The element 76 may beanother three-dimensional test instrument for example, such as anarticulated arm CMM, which may be relocated by device 30. Acommunication link 124 between the computer 74 and the element 76 may bewired or wireless. An operator sitting on a remote computer 74 may makea connection to the Internet, represented by cloud 76, over an Ethernetor wireless link, which in turn connects them to processor 78 over anEthernet or wireless link. In this way, user may control the action of aremote device, such as a laser tracker.

Referring now to FIG. 4, an embodiment of payload structure 46 within adevice 30 is shown having a tracker portion 34 and a scanner portion 36.The portions 34 and 36 are integrated to emit light from the tracker andscanner portions over a substantially common optical inner beam path,which is represented in FIGS. 1 and 12-14 by the beam of light 52.However, although the light emitted by the tracker and scanner portionstravel over a substantially common optical path, in an embodiment, thebeams of light from the tracker and scanner portions are emitted atdifferent times. In another embodiment, the beams are emitted at thesame time.

The tracker portion 34 includes a light source 126, an isolator 128, afiber network 136, ADM electronics 140, a fiber launch 130, a beamsplitter 132, and a position detector 134. In an embodiment, the lightsource 126 is emits visible light. The light source may be, for example,a red or green diode laser or a vertical cavity surface emitting laser.The isolator may be a Faraday isolator, and attenuator, or any othersuitable device capable of sufficiently reducing the amount of lighttransmitted back into the light source 126. Light from the isolator 128travels into the fiber network 136. In one embodiment, the fiber network136 is the fiber network shown in FIG. 6 as will be discussed in moredetail below. The position detector 134 is arranged to receive a portionof the radiation emitted by the light source 126 and reflected by thetarget 58. The position detector 134 is configured to provide a signalto the controller 64. The signal is used by the controller 64 toactivate the motors 51, 55 to steer the light beam 52 to track thetarget 58.

Some of light entering the fiber network 136 is transmitted over opticalfiber 138 to the reference channel of the ADM electronics 140. Anotherportion of the light entering fiber network 136 passes through the fibernetwork 136 and the beam splitter 132. The light arrives at a dichroicbeam splitter 142, which is configured to transmit light at thewavelength of the ADM light source. The light from the tracker portion34 exits the payload structure 46 via an aperture 146 along optical path144. The light from the tracker portion 34 travels along optical path144, is reflected by the target 58, and returns along the optical path144 to re-enter the payload structure 46 through the aperture 146. Thisreturning light passes through dichroic beam splitter 142 and travelsback into the tracker portion 34. A first portion of the returning lightpasses through the beam splitter 132 and into fiber launch 130 and intothe fiber network 136. Part of the light passes into optical fiber 148and passes into the measure channel of the ADM electronics 140. A secondportion of the returning light is reflected off of the beam splitter 132and into position detector 134.

In one embodiment, the ADM electronics 140 is that shown in FIG. 5. TheADM electronics 140 includes a frequency reference 3302, a synthesizer3304, a measure detector 3306, a reference detector 3308, a measuremixer 3310, a reference mixer 3312, conditioning electronics 3314, 3316,3318, 3320, a divide-by-N prescaler 3324, and an analog-to-digitalconverter (ADC) 3322. The frequency reference, which may be an ovencontrolled crystal oscillator for example, sends a reference frequencyf_(REF), such as 10 MHz for example, to the synthesizer which generatestwo electrical signals—one signal at frequency f_(RF) and two signals atfrequency f_(LO). The signal f_(RF) goes to the light source 126. Thetwo signals at frequency f_(LO) go to the measure mixer 3310 and thereference mixer 3312. The light from optical fibers 138, 148 enter thereference and measure channels respectively. Reference detector 3308 andmeasure detector 3306 convert the optical signals into electricalsignals. These signals are conditioned by electrical components 3316,3314, respectively, and are sent to mixers 3312, 3310 respectively. Themixers produce a frequency f_(IF) equal to the absolute value off_(LO)−f_(RF). The signal f_(RF) may be a relatively high frequency,such as 2 GHz, while the signal f_(IF) may have a relatively lowfrequency, such as 10 kHz.

The reference frequency f_(REF) is sent to the prescaler 3324, whichdivides the frequency by an integer value. For example, a frequency of10 MHz might be divided by 40 to obtain an output frequency of 250 kHz.In this example, the 10 kHz signals entering the ADC 3322 would besampled at a rate of 250 kHz, thereby producing 25 samples per cycle.The signals from ADC 3322 are sent to a data processor 3400, such as oneor more digital signal processors for example.

The method for extracting a distance is based on the calculation ofphase of the ADC signals for the reference and measure channels. Thismethod is described in detail in U.S. Pat. No. 7,701,559 ('559 patent)to Bridges et al., the contents of which are herein incorporated byreference. The calculation includes the use of equations (1)-(8) of the'599 patent. In addition, when the ADM first begins to measure a target,the frequencies generated by the synthesizer are changed some number oftimes (for example, three times), and the possible ADM distances arecalculated in each case. By comparing the possible ADM distances foreach of the selected frequencies, an ambiguity in the ADM measurement isremoved. The equations (1)-(8) of the '599 patent combined withsynchronization methods and Kalman filter methods described in the '599patent enable the ADM to measure a moving target. In other embodiments,other methods of obtaining absolute distance measurements may be used,such as pulsed time of flight methods for example.

An embodiment of the fiber network 136 in FIG. 4 is shown as fibernetwork 420A in FIG. 6. This embodiment includes a first fiber coupler430, a second fiber coupler 436 and low-transmission reflectors 435,440. The first and second fiber couplers are 2×2 couplers each havingtwo input ports and two output ports. Couplers of this type are usuallymade by placing two fiber cores in close proximity and then drawing thefibers. In this way, evanescent coupling between the fibers can splitoff a desired fraction of the light to the adjacent fiber. Light travelsthrough the first fiber coupler 430 and splits between two paths, thefirst path through optical fiber 433 to the second fiber coupler 436 andin the second path through optical fiber 422 and fiber length equalizer423. Fiber length equalizer 423 connects to fiber 138 in FIG. 4, whichtravels to the reference channel of the ADM electronics 140. The purposeof the fiber length equalizer 423 is to match the length of opticalfibers traversed by the light in the reference channel to the length ofoptical fibers traversed by light in the measure channel. Matching thefiber lengths in this way reduces ADM errors caused by changes in theambient temperature. Such errors may arise because the effective opticalpath length of an optical fiber is equal to the average index ofrefraction of the optical fiber times the length of the fiber. Since theindex of refraction of the optical fibers depends on the temperature ofthe fiber, a change in the temperature of the optical fibers causeschanges in the effective optical path lengths of the measure andreference channels. If the effective optical path length of the opticalfiber in the measure channel changes relative to the effective opticalpath length of the optical fiber in the reference channel, the resultwill be an apparent shift in the position of the target 58, even if thetarget 58 is kept stationary. To avoid this problem, two steps aretaken. First the length of the fiber in the reference channel ismatched, as nearly as possible, to the length of the fiber in themeasure channel. Second, the measure and reference fibers are routedside-by-side to the extent possible to ensure that the optical fibers inthe two channels are subject to nearly the same changes in temperature.

The light travels through optical fiber 433 to the second fiber opticcoupler 436 and splits into two paths, the first path to thelow-reflection fiber terminator 440 and the second path to optical fiber438, from which it exits the fiber network.

Another embodiment of the fiber network 136 is shown in FIG. 7. In thisembodiment, the fiber network 136 includes a first fiber coupler 457, asecond fiber coupler 463, two low-reflection terminations 462, 467, anoptical switch 468, a retroreflector 472, and an electrical input 469 tothe optical switch. The optical switch may be several types. Acommercially available and relatively inexpensive type is themicro-electro-mechanical system (MEMS) type. This type may use smallmirrors constructed for example as a part of a semiconductor structure.Alternatively, the switch could be a modulator, which is available forvery fast switching at certain wavelengths and at a cost that issomewhat higher than a MEMS type switch. Switches may also beconstructed of optical attenuators, which may respond to electricalsignals and may be turned on and off by electrical signals sent to theattenuators. A description of the specifications that may be consideredin selecting fiber-optic switches is given in U.S. Published PatentApplication Publication No. 2011/0032509 to Bridges, the contents ofwhich are incorporated by reference. In general, to obtain the desiredperformance and simplicity, the switch may be a fiber-optic switch. Itshould be appreciated that the optical switching concept described aboveshould perform equally well in a fiber network based on two colors.

The fiber network 136 contains an optical switch 468 and aretroreflector 472. Ordinarily the light travels from fiber 465 throughthe upper port of optical switch 468 and out optical fiber 470. However,on occasion, when the laser tracker is not measuring a target, theoptical switch diverts the optical signal from the optical fiber 465 tothe optical fiber 471 and into the retroreflector 472. The purpose ofswitching the light to retroreflector 472 is to remove any thermal driftthat may have occurred in the components of the ADM system. Suchcomponents might include, for example, opto-electronic components suchas optical detectors, optical fibers of the ADM system, electricalcomponents such as mixers, amplifiers, synthesizer, andanalog-to-digital converters, and optical components such as lenses andlens mounts. For example, suppose that at a first time, the path lengthof the measure channel was found to be 20 mm longer than the referencechannel with the optical switch 468 diverting the light toretroreflector 472. Suppose that at a later time the measure channelpath length was found to be 20.003 mm longer than the reference channelpath length with the optical switch 468 diverting the light toretroreflector 472. The ADM data processor would subtract 0.003 mm fromsubsequent ADM readings. It should be understood that this procedurewould start anew whenever the tracker set the ADM value at a homeposition of the laser tracker.

In an embodiment, the retroreflector 472 is a fiber-optic retroreflector472A of FIG. 8. This type of retroreflector 472 is typically a ferrulewith the optical fiber polished at the end of the ferrule and coveredwith a coating 473, which might be gold or multiple layers of thindielectric films, for example. In another embodiment, the retroreflector472 is a free space retroreflector 472B of FIG. 9 that includes acollimator 474 and a retroreflector 476, which might be a cube-cornerretroreflector slug, for example.

Still another embodiment of fiber network 136 is shown in FIG. 10. Inthis embodiment, the fiber network 136 includes a first fiber coupler1730, a second fiber coupler 1740, a third fiber coupler 1750 and threelow-reflection terminations 1738, 1748, 1758. The light from opticalfiber 1781 enters fiber network 136 at the input port. The light travelsthrough a first fiber coupler 1730. A portion of the light travelsthrough optical fiber 138 and fiber length compensator for 423 beforeentering the reference channel of ADM electronics 140. Some of the lighttravels through a second fiber coupler 1740 and a third fiber coupler1750 before passing out of the fiber network onto optical fiber 1753.The light from optical fiber 1743 enters into the third fiber coupler1750, where it is combined with the light from a second light source(not shown) via optical fiber 1790 to form a composite light beam thattravels on optical fiber 1753. The optical coupler 1750 is a dichroiccoupler because it is designed to use two wavelengths. After thecomposite light beam carried in optical fiber 1753 travels out of thelaser tracker and reflects off target 58, it returns to the fibernetwork 136. The light from the first light source passes through thethird fiber coupler 1750, the second fiber coupler 1740, and entersoptical fiber 148, which leads to the measure channel of the ADMelectronics 140. The light from the second light source (not shown)returns to optical fiber 1790 and travels back toward the second lightsource (not shown).

The couplers 1730, 1740, and 1750 may be of the fused type. With thistype of optical coupler, two fiber core/cladding regions are broughtclose together and fused. Consequently, light between the cores isexchanged by evanescent coupling. In the case of two differentwavelengths, it is possible to design an evanescent coupling arrangementthat allows complete transmission of a first wavelength along theoriginal fiber and complete coupling of a second wavelength over to thesame fiber. Ordinarily there is not a complete (100 percent) coupling ofthe light into the coupler 1750. However, fiber-optic couplers thatprovide good coupling for two or more different wavelengths arecommercially available at common wavelengths such as 980 nm, 1300 nm,and 1550 nm. In addition, fiber-optic couplers may be commerciallypurchased for other wavelengths, including visible wavelengths, and maybe designed and manufactured for other wavelengths. For example, in FIG.10, it is possible to configure a fiber optic coupler 1750 so that thefirst light at its first wavelength travels from optical fiber 1743 tooptical fiber 1753 with low optical loss. At the same time, thearrangement may be configured to provide for a nearly complete couplingof the second light on optical fiber 1790 over to the optical fiber1753. Hence it is possible to transfer the first light and the secondlight through the fiber optic coupler and onto the same fiber 1753 withlow loss. Optical couplers are commercially available that combinewavelengths that differ widely in wavelength. For example, couplers arecommercially available that combine light at a wavelength of 1310 nmwith light at a wavelength of 660 nm. For propagation over longdistances with propagation of both wavelengths in a single transversemode while having relatively low loss of optical power duringpropagation through the optical fiber, it is generally desirable thatthe two wavelengths be relatively close together. For example, the twoselected wavelengths might be 633 nm and 780 nm, which are relativelyclose together in wavelength values and could be transmitted through asingle-mode optical fiber over a long distance without a high loss. Anadvantage of the dichroic fiber coupler 1750 within the fiber network136 is that it is more compact than a free space beam splitter. Inaddition, the dichroic fiber coupler ensures that the first light andthe second light are very well aligned without requiring any specialoptical alignment procedures during production.

Referring back to FIG. 4, the scanner portion 36 may be embedded in ascanner such as that shown in FIG. 11 discussed herein below forexample. The light, such as infrared light at about 1550 nm for example,from the scanner portion 36 travels along optical path 150 to thedichroic mirror 142. The dichroic mirror 142 is configured to reflectthe light from the scanner while allowing light from the laser trackerto pass through. The light from scanner portion 36 travels to the target58 and returns along optical path 152 to annular aperture 154. Thereturning light passes through the annular aperture 154 and along anouter beam path to reflect off of dichroic mirror 142 along optical path156 back to the scanner portion 36. In one embodiment, the outer beampath (defined by the annular aperture 154) is coaxial with the innerbeam path (defined by the aperture 146). Advantages may be gained byreturning the scanner light through the annular aperture 154 to avoid ofunwanted light from the aperture 146 that could corrupt the lightreflected off of target 58.

In the exemplary embodiment the aperture 146 and the annular aperture154 are concentrically arranged. In this embodiment, the aperture 146has a diameter of about 15 mm and the annular aperture 154 has an innerdiameter of 15 mm and an outer diameter of 35 mm.

It should be appreciated that in the exemplary embodiment the dichroicmirror 142 is positioned at the gimbal point 50. In this manner, lightfrom both the scanner portion 36 and the tracker portion 34 may appearto originate from the same point in the device 30. In the exemplaryembodiment, the tracker portion 34 emits a visible laser light, whilethe scanner portion 36 emits a light in the near infrared spectrum. Thelight from tracker portion 34 may have a wavelength about 700 nm and thelight from the scanner portion 36 may have a wavelength of about 1550nm.

One embodiment of the scanner portion 36 is shown in FIG. 11. In thisembodiment, the scanner portion 36 includes a light emitter 160 thatemits a light beam 162 through a collimator 165. The light emitter 160may be a laser diode that emits light at a wavelength in the range ofapproximately 1550 nm. It should be appreciated that otherelectromagnetic waves having, for example, a lesser or greaterwavelength may be used. Light beam 162 may be intensity modulated oramplitude modulated, such as with a sinusoidal or rectangular waveformmodulation signal. The light beam 162 is sent to the dichroic beamsplitter 142, which reflects the light beam 162 through the aperture 146and onto the target 58. In the exemplary embodiment, the light beam 162is reflected off of a mirror 170 and a dichroic beam splitter 172 toallow the light beam 162 to travel along the desired optical path oflight beams 52, 150. As will be discussed in more detail below, the useof a dichroic beam splitter 172 provides advantages in allowing for theincorporation of a color camera 168 that acquires images duringoperation. In other embodiments, the light emitter 160 may be arrangedto directly transmit the light onto dichroic mirror 142 without firstreflecting off a mirror 170 and a dichroic beam splitter 172.

As shown in FIGS. 4 and 11, the outgoing light from the tracker andscanner portions 34, 36 both pass through the same aperture 146. Thelight from these tracker and scanner portions 34, 36 are substantiallycollinear and travel along the optical path of light beam 52 of FIG. 1.On the return path, the light from the tracker portion 34 will have beenreflected by a retroreflector target and hence is approximatelycollimated when it returns to the device 30. The returning beam oftracker light passes back through aperture 146, which is the sameaperture through which it exited the device 30. On the other hand, thelight from the scanner portion 36 usually strikes a diffusely scatteringobject 59 and spreads over a wide angle as it returns. A small portionof the reflected light passes through an annual aperture 154 positionedto have its inner diameter to be the same as (or concentric with) theouter diameter of the aperture 146. The returning light 163 reflects offthe dichroic beam splitter, passes as beam of light 163 through the lens160, reflects off reflective surfaces 180, 178, 176, and passes througha collection of lenses within the light receiver 182 before arriving atan optical detector. The returning scanner light is directed through theannular aperture 154 without including any light that may pass backthrough the inner aperture 146. This provides advantages since theoptical power of the outgoing beam is so much greater than the lightreturned by the object that it is desirable to avoid having backreflections off optical elements along the path of the inner aperture146.

In an embodiment, an optional color camera 168 is arranged so that aportion of the light reflected by the object passes through the dichroicmirror 172 into a color camera 168. The coatings on the dichroic mirrorare selected to pass visible wavelengths picked up by a color camerawhile reflecting light at the wavelength emitted by the light emitter160. The camera 168 may be coupled to the receiver lens 160 with anadhesive or within a recess for example. The color camera 168 allowscolor pictures to be acquired, usually by making a few discrete steps ata time following acquisition of data points by the distance meter withinthe scanner.

In an embodiment, a mask 174 is coaxially arranged on the optical axisbehind the receiver lens 160. The mask 174 has a large area in which thereturning light beam 163 is allowed to pass unimpeded. The mask 174 hasshaded regions positioned radially outward from the optical axis inorder to reduce intensity of the returning light beam 163 in such a wayas to make the intensities of the returning light more nearly comparablefor different object distances from the device 30.

In an embodiment, a rear mirror 176 is arranged on the optical axisbehind the mask 174. The rear mirror 176 reflects the returning lightbeam 163 that is refracted by the receiver lens 166 towards a centralmirror 178. The central mirror 178 is arranged in the center of the mask174 on the optical axis. In embodiments having a color camera 168, thisarea may be shadowed by the color camera 168. The central mirror 178 maybe an aspherical mirror which acts as both a negative lens (i.e.increases the focal length) and as a near-field-correction lens (i.e.shifts the focus of the returning light beam 163 which is reflected bythe target). Additionally, a reflection is provided only to the extentthat the returning light beam 163 passes the mask 174 arranged on thecentral mirror 178. The central mirror 178 reflects the returning lightbeam through a central orifice 180 in rear mirror 176.

A light receiver 182 having an entrance diaphragm, a collimator withfilter, a collecting lens and an optical detector, is arranged adjacentrear mirror 176 opposite the mask 174. In one embodiment, a mirror 184deflects the returning light beam 163 by 90°.

In one embodiment, the scanner portion 36 may have one or moreprocessors 186, which may be the same as or supplementary to the scannerprocessor electronics 96 of FIG. 3. The processor 186 performs controland evaluation functions for the scanner portion 36. The processor 186is coupled to communicate with the light emitter 160 and light receiver182. The processor 186 determines for each measured point the distancebetween the device 30 and the target 58 based on the time of flight ofthe emitted light beam 162 and the returning light beam 163. In otherembodiments, the processor 186 and its functionality may be integratedinto the controller 64, which may correspond to the scanner processor96, the master processor 78, the computer 74, or the networked elements76 of FIG. 3.

The optical distance meters of the tracker portion 34 and scannerportion 36 may determine distance using the principle of time-of-flight.It should be understood that the term time-of-flight is used here toindicate any method in which modulated light is evaluated to determinedistance to a target. For example, the light from the tracker portion 34or scanner portion 36 may be modulated in optical power (intensitymodulation) using a sinusoidal wave. The detected light may be evaluatedto determine the phase shift between a reference and a measure beam todetermine distance to a target. In another embodiment, the optical powerof the light may be modulated by pulsed light having an approximatelyrectangular shape. In this case, the leading edge of the pulse may bemeasured on the way out of the device 30 and upon return to the device30. In this case, the elapsed time is used to determine distance to thetarget. Another method involves changing the polarization state of lightas a function of time by means of modulation of an external modulatorand then noting the frequency of modulation at which returning light isextinguished after it is passed through a polarizer. Many other methodsof measuring distance fall within the general time-of-flight category.

Another general method of measuring distance is referred to as acoherent or interferometric method. Unlike the previous method in whichthe optical power of a beam of light is evaluated, coherent orinterferometric methods involve combining two beams of light that aremutually coherent so that optical interference of the electric fieldsoccurs. Addition of electric fields rather than optical powers isanalogous to adding electrical voltages rather than electrical powers.One type of coherent distance meters involves changing the wavelength oflight as a function of time. For example, the wavelength may be changedin a sawtooth pattern (changing linearly with periodic repetitions). Adevice made using such a method is sometimes referred to as frequencymodulated coherent laser (FMCL) radar. Any method, coherent ortime-of-flight, may be used in the distance meters of the trackerportion 34 and scanner portion 36.

Referring now to FIGS. 12-14, an embodiment of the device is shown withfront covers removed and some optical and electrical components omittedfor clarity. In this embodiment the device 30 includes a gimbal assembly3610, which includes a zenith shaft 3630 and an optics bench assembly3620 having a mating tube 3622. The zenith shaft includes a shaft 3634and a mating sleeve 3632. The zenith shaft 3630 may be fabricated from asingle piece of metal in order to improve rigidity and temperaturestability. FIG. 14 shows an embodiment of an optics bench assembly 3720and zenith shaft 3630. The optics bench assembly 3720 includes a mainoptics assembly 3650 and a secondary optics assembly 3740. The housingfor the main optics assembly 3650 may be fabricated out of single pieceof metal to improve rigidity and temperature stability and includes amating tube 3622. In an embodiment, the central axis of the mating tube3622 is aligned with the central axis of the mating sleeve 3632. In oneembodiment, four fasteners 3664 attach secondary optics assembly 3740 tothe main optics assembly 3650. The mating tube 3622 is inserted into themating sleeve 3632 and held in place by three screws 3662. In anembodiment, the mating tube 3622 is aligned with this mating sleeve 3632by means of two pins on one end of meeting tube 3622, the pins fittinginto holes 3666.

Although the gimbal assembly 3610 is designed to hold an optical bench3620, other types of devices such as a camera, a laser engraver, a videotracker, a laser pointer and angular measuring device, or a LightDetection and Ranging (LIDAR) system could be disposed on the zenithshaft 3630. Due to the alignment registration provided by the matingsleeve 3632, such devices could be easily and accurately attached to thegimbal assembly 3610. In the exemplary embodiment, the tracker portion34 is arranged within the main optics assembly 3650, while the scannerportion 36 is disposed in the secondary optics assembly 3740. Thedichroic mirror 142 is arranged in the main optics assembly 3650 asshown in FIG. 14.

In operation, the device 30 has two modes of operation, as shown in FIG.15 and FIG. 16, depending on the level of accuracy desired. The firstmode (FIG. 15) uses the tracker portion 34 in combination with acooperative target 58, such as a retroreflector target, which might be aspherically mounted retroreflector (SMR) for example. In this firstmode, the device 30 emits a light beam 52 that virtually passes throughthe gimbal point 50, dichroic mirror 142, and aperture 146 towardstarget 58. The light 52 strikes the target 58, and a portion of thelight travels back along the same optical pathway through the aperture146 and the dichroic mirror 142 to the tracker portion 34. The device 30then determines the distance from the device 30 to the target 58 asdiscussed herein above with respect to FIGS. 4-10. In an embodiment,during this first mode of operation, the scanner portion 36 does notoperate.

In the second mode of operation shown in FIG. 16, the scanner portion 36emits a light beam 162 that reflects off of the dichroic mirror 142 andis emitted through the aperture 146 toward the target 58. It should beappreciated that the scanner portion 36 may measure the distance to anoncooperative target and does not need a target such as aretroreflector to obtain measurements. The light reflects (scatters) offof the target 58 and a portion 163 of the light returns through theannular aperture 154. As discussed above it is desirable for thereturning light 163 to pass through the annular aperture 154 since thisprovides advantages in reducing back reflections from the optics whichcould corrupt the returning light signal. The returning light 163reflects off of the dichroic mirror 142 back to the scanner portion 36whereupon the distance from the device 30 to the target 58 is determinedas discussed herein above with respect to FIG. 11. The scanner portion36 operates continuously as the payload structure 46 is rotatedsimultaneously about the azimuth axis 44 and the zenith axis 48. In theexemplary embodiment, the path followed by the light beam 162 proceedsin a single direction (e.g. does not reverse) as the payload 46 rotatesabout the axis 44, 48. This pathway may be achieved by continuouslyrotating each of the zenith and azimuth motors in a single direction.Another way of stating this is to say that in the second mode, the beamis directed to an object surface while the zenith and azimuth angles arecontinuously and monotonically changing. Notice that the beam may besteered rapidly about one axis (either zenith or azimuth axis) whilesteered relatively more slowly about the other axis. In one embodiment,the movement of the payload 46 cases results in the light beam 162following a spiral pathway.

It should be appreciated that having the scanner portion 36 operate suchthat the path of the light beam 162 does not have to reverse providesseveral advantages over scanners that follow a raster-type pattern or arandom pattern. First, a large amount of data may be efficientlycollected since a reversal of direction is not required. As a result,the scanner portion 36 can effectively scan a large area while acquiringdata at a high sample rate, such as more than one millionthree-dimensional points per second. Second, by proceeding continuouslyin a single direction, in the event that the light beam intersects witha person, the total energy deposited on an area of the person is small.This allows for a more desirable IEC 60825-1 laser categorization.

In one embodiment, the tracker portion 34 emits a light beam 52 in thevisible light spectrum. In this embodiment, the tracker portion 34 mayemit the light beam 52 as the scanner portion 36 emits light 162. Thisprovides advantages since the visible light 52 from the tracker portion34 provides a visible reference for the operator.

Turning now to FIGS. 17-18, a method of operating the device 30 isshown. The method 190 starts with selecting a mode of operation totracker portion 34 in block 192. The method then proceeds to block 194where the tracker portion 34 is activated. The gimbal mechanism is thenmoved about the zenith and azimuth axes in block 196 to steer the lightbeam toward the target 58. The light reflects off the cooperative target58 and returns to the device 30 through aperture 146 in block 198. Thedevice 30 then calculates the distance from the device 30 the target 58in block 200. The azimuth and zenith angles are determined in block 202and the three-dimensional coordinates (distance and two angles) for themeasured point are determined. This process may be repeated until allthe desired measured points have been determined.

Referring now to FIG. 18 the method 203 is shown wherein the scannerportion 36 is selected in block 204. The method 203 then proceeds toblock 206 where the scanner portion 36 is activated. Where it isdesirable to provide a visible reference light, the light from trackerportion 34 is activated in block 208. The light is transmitted from thescanner portion 36 through the aperture 146 towards the target 58. Inthe exemplary embodiment, the light from the scanner portion 36 isemitted along a pathway in a single direction (such as a spiral shape)without reversing direction as indicated in block 209. The light isreflected off of the target 58 and back towards the device 30. Thereturning light is received through the annular aperture 154 in block210. The distance from the device 30 the target 58 is determined inblock 212. The azimuth and zenith angles are determined in block 214 andcoordinates (distance and two angles) to the measured point on target 58are determined.

The method of directing the beam of light from the scanner portion 36 tothe object 59 may be carried out in different ways. In a firstembodiment, light from the scanner portion 36 is directed with thegimbal assembly 3610 facing in the same general direction. In this modeof operation, the beam is directed to any desired point. In a secondembodiment, light from the scanner portion 36 is directed with thegimbal assembly 3610 spinning at a relatively rapid constant rate aboutan axis, which might be either the azimuth axis or the zenith axis. Theother axis is also moved but at a relatively slower rate. In this way,the beam is directed in a slow spiral. With the second embodiment, athorough scan of a large volume can be quickly performed. Anotheradvantage of the second embodiment is that the constantly moving beamintercepts the pupil of the human eye for a shorter time during itscontinual movement. Because of this, higher laser powers can be usedwhile providing a desired IEC 60825-1 categorization.

Referring now to FIG. 19, another embodiment of the device 30 is shownhaving a first absolute distance meter within the tracker portion 34 anda second absolute distance meter within the scanner portion 36, theportions 34 and 36 coupled to a payload structure 46. In thisembodiment, the tracker portion 34 and the scanner 36 do not emit lightover a common optical pathway. The tracker portion 34 is arranged todirect the light beam 52 in a first radial direction while the scanner36 is arranged to direct the light beam 162 in a second radial directiontoward a surface 58′. The first radial direction and second radialdirection define an angle θ therebetween. In the exemplary embodiment,the angle θ is 90 degrees. In other embodiments, the angle θ is between5 degrees and 180 degrees. However, any suitable angle may be used whichallows the tracker portion 34 and the scanner portion 36 to bepositioned within the payload structure 46. It should be appreciatedthat as the payload structure 46 is rotated about the azimuth axis 44,the tracker portion 34 and the scanner 36 will be oriented on the sameazimuth angle.

Referring now to FIG. 20, another embodiment of the device 30 is shownhaving a tracker portion 34 and a scanner portion 36. In thisembodiment, the tracker portion is oriented in parallel with the scannerportion 36 and uses a mirror 216 to reflect the light 52 towards thedichroic beam splitter 142. In this embodiment, the dichroic beamsplitter 142 is configured to reflect the light 52 while allowing thelight 162 from the scanner portion 36 to pass through.

The light beams 52, 162 pass through an aperture 146 and are directedalong the optical axis A toward an angled rotating mirror 218 that isarranged to rotate about a horizontal axis 48. The outbound light 52,162 reflects off of the mirror at the center C₁₀ where it is reflectedoff and deflected towards the target 58 (for the tracker portion) or thesurface 58′ (for the scanner portion). The center C₁₀ defines the originof the reference system. The reflected light from the target 58 orsurface 58′ is reflected back off of the rotary mirror 218 and backtoward the aperture 146. The light 52 reflects off of the rotary mirror218 at the center C₁₀ and back through the aperture 146. The light 52reflects off of dichroic mirror 142 and mirror 216 before returning tothe tracker portion 34. The returning light 163 reflects off the rotarymirror 218 and passes through the annular aperture 154 before returningto the scanner 36.

The direction of the emitted light 52, 162 and the reflected lightresults from the angular positions of the rotary mirror 218 about thehorizontal axis 48 and vertical axis 44. The angular positions aremeasured by encoders 54, 56 respectively. It should be appreciated thatin one mode of operation, the measurements by the tracker portion 34 andscanner portion 36 are performed by the means of a fast rotation of themirror 16 and the slow rotation of the payload structure 46. Thus, thewhole space may be measured, step by step, as the device progresses in acircle.

In an embodiment, the beam of light from the scanner is adjustablyfocused rather than collimated. In geometrical optics, a focused beam oflight is brought to a point, but in reality, the beam of light isbrought to a beam waist near the calculated focus position. At the beamwaist position, the width of the beam is at its smallest as the beampropagates.

One advantage of sending a focused beam of light from the scanner isthat a smaller beam can more accurately determine 3D coordinates atedges. For example, a smaller focused beam permits more accuratedetermination of hole diameter or of feature size. Another advantage ofsending a focused beam of light from the scanner is that a focused beamcan be steered to find the position of maximum reflectance of light froma tooling ball retroreflector, which is simply a shiny/highly-reflectivemetallic sphere. Such a method of directing a beam of light from thescanner to the tooling ball permits accurate determination of distanceand angles to the tooling ball. Because of this, the tooling ball can beused as a target. With a device that combines scanner and trackerfunctionality, as illustrated herein, two types of targets are then madeavailable: SMRs and tooling balls. The use of two different types oftargets provides an easy method for getting the tracker and the scannersystems in the same frame of reference since the SMRs and tooling ballscan both be held in the same magnetic nests distributed throughout anenvironment.

In an embodiment, an adjustable focusing element 39 is added to otherelements of the scanner 36. This additional adjustable focusing elementis shown in FIGS. 21-26. FIG. 21 is similar to FIG. 4 except that thescanner 36 is shown to have two internal elements—scanner elements 37and adjustable focusing mechanism 39. FIG. 22 is similar to FIG. 11except that an adjustable focusing mechanism 39 is included in thescanner 36. FIGS. 23, 24 are similar to FIGS. 15, 16 except that thescanner 36 is shown to include scanner elements 37 and adjustablefocusing mechanism 39. FIG. 25 is similar to FIG. 19 except the scanner36 is shown to include scanner elements 37 and adjustable focusingmechanism 39.

In an embodiment, the adjustable focusing mechanism 39 includes somebasic lens elements, which may include optional elements 2604, 2606. Inaddition, the adjustable focusing mechanism 39 includes a lens element2602 attached to a motorized adjustment stage 2610 configured to movethe lens 2602 back and forth to obtain the desired adjustment. In anembodiment, the scanner electronics 96 of FIG. 3 provides the electricalcontrol of the motorized adjustment stage 2610.

Many types of lens assemblies and adjustment methods are known in theart for providing adjustable focus in a lens assembly. It is understoodto one of ordinary skill in the art that any such methods may be used toprovide adjustable focus in the present invention.

While the invention has been described in detail in connection with onlya limited number of embodiments, it should be readily understood thatthe invention is not limited to such disclosed embodiments. Rather, theinvention can be modified to incorporate any number of variations,alterations, substitutions or equivalent arrangements not heretoforedescribed, but which are commensurate with the spirit and scope of theinvention. Additionally, while various embodiments of the invention havebeen described, it is to be understood that aspects of the invention mayinclude only some of the described embodiments. Accordingly, theinvention is not to be seen as limited by the foregoing description, butis only limited by the scope of the appended claims. Moreover, the useof the terms first, second, etc. do not denote any order or importance,but rather the terms first, second, etc. are used to distinguish oneelement from another. Furthermore, the use of the terms a, an, etc. donot denote a limitation of quantity, but rather denote the presence ofat least one of the referenced item.

The invention claimed is:
 1. A coordinate measurement device comprising:an optical delivery system; a first absolute distance meter including afirst light source, a first optical detector, and a first electricalcircuit, the first light source configured to send a first light throughthe optical delivery system to a retroreflector target, the firstoptical detector further configured to generate a first electricalsignal in response to the first light reflected by the retroreflectortarget and to transmit the first electrical signal to the firstelectrical circuit, the first electrical circuit configured to determinea first distance from the coordinate measurement device to theretroreflector target based at least in part on the first electricalsignal; a second absolute distance meter including a second lightsource, an adjustable focusing mechanism, a second optical detector, anda second electrical circuit, the second light source configured to senda second light through the adjustable focusing mechanism and the opticaldelivery system to an object surface, the second optical detectorconfigured to receive a portion of the second light reflected by theobject surface and passed through the optical delivery system, thesecond optical detector further configured to generate a secondelectrical signal in response to receiving a portion of the second lightreflected by the object surface and to send the second electrical signalto the second electrical circuit, the second electrical circuitconfigured to determine a second distance from the coordinatemeasurement device to the object surface based at least in part on thesecond electrical signal; a structure operably coupled to the opticaldelivery system, the first absolute distance meter, and the secondabsolute distance meter; a first motor configured to rotate thestructure about a first axis; a first angular transducer operablycoupled to the structure, the first angular transducer configured tomeasure a first angle of rotation about the first axis; a second motorconfigure to rotate the structure about a second axis, the second axisbeing substantially perpendicular to the first axis; a second angulartransducer operably coupled to the structure, the second angulartransducer configured to measure a second angle of rotation about thesecond axis; a position detector, the position detector configured toreceive a portion of radiation emitted by the coordinate measurementdevice and reflected by the retroreflector target, the position detectorconfigured to generate a third electrical signal based at least in parton a location at which the portion of radiation strikes the positiondetector; and a processor, the processor having a non-transitorycomputer readable media configured to operate in a first mode and asecond mode, wherein the first mode includes tracking the retroreflectortarget based at least in part on the third electrical signal, anddetermining a first three-dimensional coordinate of the retroreflectortarget based at least in part on the first angle of rotation to theretroreflector target at a first position, the second angle of rotationto the retroreflector target at the first position, and the firstdistance of the retroreflector target at the first position, and whereinthe second mode includes directing the second light to the objectsurface and determining a second three-dimensional coordinate of a pointon the object surface based at least in part on the first angle ofrotation to the point on the object surface, the second angle ofrotation to the point on the object surface, and the second distance ofthe point on the object surface, the second mode further includingadjusting the adjustable focusing mechanism.
 2. The coordinatemeasurement device of claim 1 wherein: the optical delivery system hasan inner beam path and an outer beam path, the outer beam path coaxialwith the inner beam path and outside the inner beam path; the firstoptical detector is configured to receive the first light reflected bythe retroreflector target and passed through the inner beam path of theoptical delivery system; and the second optical detector is configuredto receive the second light reflected by the object surface and passedthrough the outer beam path of the optical delivery system.
 3. Thecoordinate measurement device of claim 1 wherein rotating of thestructure unidirectionally emits the second light along a pathway havinga spiral shape.
 4. The coordinate measurement device of claim 1 whereinthe optical delivery system further includes an annular aperturepositioned to receive the portion of the second light reflected by theobject surface.
 5. The coordinate measurement device of claim 4 whereinthe processor is configured to emit the first light when the secondabsolute distance meter is emitting the second light.
 6. The coordinatemeasurement device of claim 1 wherein the first light has a wavelengthof about 700 nanometers.
 7. The coordinate measurement device of claim 6wherein the second light has a wavelength of about 1550 nanometers.
 8. Acoordinate measurement device comprising: a structure; a first motorconfigured to rotate the structure about a first axis; a first angulartransducer operably coupled to the structure, the first angulartransducer configured to measure a first angle of rotation about thefirst axis; a second motor configure to rotate the structure about asecond axis, the second axis being substantially perpendicular to thefirst axis, a projection of the second axis intersecting a projection ofthe first axis in a gimbal point; a second angular transducer operablycoupled to the structure, the second angular transducer configured tomeasure a second angle of rotation about the second axis; an opticaldelivery system operably coupled to the structure; a first absolutedistance meter operably coupled to the structure, the first absolutedistance meter including a first light source, a first optical detector,and a first electrical circuit, the first light source configured tosend a first light through the optical delivery system along a portionof a first line that extends from the gimbal point to a retroreflectortarget, the first line being perpendicular to the first axis, the firstoptical detector configured to receive the first light reflected by theretroreflector target and passed through the optical delivery system,the first optical detector further configured to generate a firstelectrical signal in response to the first light reflected by theretroreflector target and to transmit the first electrical signal to thefirst electrical circuit, the first electrical circuit configured todetermine a first distance from the coordinate measurement device to theretroreflector target based at least in part on the first electricalsignal; a second absolute distance meter operably coupled to thestructure, the second absolute distance meter including a second lightsource, an adjustable focusing mechanism, a second optical detector, anda second electrical circuit, the second light source configured to senda second light through the adjustable focusing mechanism and the opticaldelivery system along a portion of a second line that extends from thegimbal point to an object surface, the second line being perpendicularto the first axis, the second line being different than the first line,the second optical detector configured to receive a portion of thesecond light reflected by the object surface and passed through theoptical delivery system, the second optical detector further configuredto generate a second electrical signal in response to receiving aportion of the second light reflected by the object surface and to sendthe second electrical signal to the second electrical circuit, thesecond electrical circuit configured to determine a second distance fromthe coordinate measurement device to the object surface based at leastin part on the second electrical signal; a position detector, theposition detector configured to receive a portion of radiation emittedby the coordinate measurement device and reflected by the retroreflectortarget, the position detector configured to generate a third electricalsignal based at least in part on a location at which the portion ofradiation strikes the position detector; and a processor, the processorhaving a non-transitory computer readable media configured to operate ina first mode and a second mode, wherein the first mode includes trackingthe retroreflector target based at least in part on the third electricalsignal, and determining a first three-dimensional coordinate of theretroreflector target based at least in part on the first angle ofrotation to the retroreflector target at a first position, the secondangle of rotation to the retroreflector target at the first position,and the first distance of the retroreflector target at the firstposition, and wherein the second mode includes rotating the structureabout the first axis and determining a second three-dimensionalcoordinate of a point on the object surface based at least in part onthe first angle of rotation to the point on the object surface, thesecond angle of rotation to the point on the object surface, and thesecond distance of the point on the object surface, the second modefurther including adjusting the adjustable focusing mechanism.
 9. Thecoordinate measurement device of claim 8 wherein the first line extendsin a first radial direction and the second line extends in a secondradial direction to define an angle therebetween, the angle beingbetween 5 degrees and 180 degrees.
 10. The coordinate measurement deviceof claim 9 wherein the angle is 90 degrees.
 11. The coordinatemeasurement device of claim 8 wherein the first light has a wavelengthof about 700 nanometers.
 12. The coordinate measurement device of claim9 wherein the second light has a wavelength of about 1550 nanometers.13. The coordinate measurement device of claim 8 wherein the opticaldelivery system further includes an annular aperture positioned toreceive a portion of the second light reflected by the object surface.14. The coordinate measurement device of claim 8 wherein the processoris configured to emit the first light when the second absolute distancemeter is emitting the second light.
 15. A coordinate measurement devicecomprising: an optical delivery system; a first absolute distance meterincluding a first light source, a first optical detector, and a firstelectrical circuit, the first light source configured to send a firstlight through the optical delivery system to a retroreflector target,the first optical detector configured to receive the first lightreflected by the retroreflector target and passed through the opticaldelivery system, the first optical detector further configured togenerate a first electrical signal in response to the first lightreflected by the retroreflector target and to transmit the firstelectrical signal to the first electrical circuit, the first electricalcircuit configured to determine a first distance from the coordinatemeasurement device to the retroreflector target based at least in parton the first electrical signal; a second absolute distance meterincluding a second light source, an adjustable focusing mechanism, asecond optical detector, and a second electrical circuit, the secondlight source configured to send a second light through the adjustablefocusing mechanism and the optical delivery system to an object surface,the second optical detector configured to receive a portion of thesecond light reflected by the object surface and passed through theoptical delivery system, the second optical detector further configuredto generate a second electrical signal in response to receiving theportion of the second light reflected by the object surface and to sendthe second electrical signal to the second electrical circuit, thesecond electrical circuit configured to determine a second distance fromthe coordinate measurement device to the object surface based at leastin part on the second electrical signal; a structure operably coupled tothe optical delivery system, the first absolute distance meter, and thesecond absolute distance meter, the structure including a mirror mountedfor rotation, the mirror being arranged within an optical path of thefirst light and the second light; a first motor configured to rotate thestructure about a first axis; a first angular transducer operablycoupled to the structure, the first angular transducer configured tomeasure a first angle of rotation about the first axis; a second motorconfigured to rotate the mirror about a second axis, the second axisbeing substantially perpendicular to the first axis; a second angulartransducer operably coupled to the mirror, the second angular transducerconfigured to measure a second angle of rotation about the second axis;a position detector, the position detector configured to receive aportion of radiation emitted by the coordinate measurement device andreflected by the retroreflector target, the position detector configuredto generate a third electrical signal based at least in part on alocation at which the portion of radiation strikes the positiondetector; and a processor, the processor having a non-transitorycomputer readable media configured to operate in a first mode and asecond mode, wherein the first mode includes tracking the retroreflectortarget based at least in part on the third electrical signal, anddetermining a first three-dimensional coordinate of the retroreflectortarget based at least in part on the first angle of rotation to theretroreflector target at a first position, the second angle of rotationto the retroreflector target at the first position, and the firstdistance of the retroreflector target at the first position, and whereinthe second mode including rotating the structure about the first axisand determining a second three-dimensional coordinate of a point on theobject surface based at least in part on the first angle of rotation tothe point on the object surface, the second angle of rotation to thepoint on the object surface, and the second distance of the point on theobject surface, the second mode further including adjusting theadjustable focusing mechanism.
 16. The coordinate measurement device ofclaim 15 wherein in the second mode the first motor rotates thestructure at a first speed and the second motor rotates the mirror at asecond speed, the second speed being greater than the first speed. 17.The coordinate measurement device of claim 16 wherein the second modeincludes rotating the structure unidirectionally about the first axis.18. The coordinate measurement device of claim 17 wherein theunidirectional rotation of the first axis emits the second light along apathway having a spiral shape.
 19. The coordinate measurement device ofclaim 15 wherein the first light has a wavelength of about 700nanometers.
 20. The coordinate measurement device of claim 19 whereinthe second light has a wavelength of about 1550 nanometers.
 21. Thecoordinate measurement device of claim 15 wherein the optical deliverysystem further includes an annular aperture positioned to receive aportion of the second light reflected by the object surface.
 22. Thecoordinate measurement device of claim 15 wherein the processor isconfigured to emit the first light when the second absolute distancemeter is emitting the second light.